In a wastewater collection service area, many pump stations often pump wastewater to a treatment facility or to a master pump station through a main. The main may sometimes be gravity fed, or may be under pressure, i.e., a force main. The mains may be used to move wastewater (under pressure in some instances) to a wastewater treatment plant. Typically, force mains may be used to move wastewater over terrain that is not conducive to gravity flow. A typical wastewater pump station may house more than one pump. The number and size of the pumps at each station may be determined by the amount of wastewater inflow to that station, and by the amount of storage capacity in a wet well. There is normally no coordination of activity between pumping stations. Pump operations at a given wastewater pump station are typically controlled locally. In other words, the pumps within the wastewater pump stations are not in communication with one another and do not operate based on any coordination with one another. When the influent in the wet well of a wastewater pump station reaches a certain predetermined level, a sensor may trigger one of the pumps to start. If the pump's action is not sufficient to handle the inflow of wastewater, additional pumps may be activated to manage the inflow of wastewater into the wet well. When the wet well level lowers to a desired level, another sensor may cause the pump(s) to turn off.
Most wastewater is generated during two or three peak periods of daily activity. These peak periods may occur in the morning when families are rising for the day and in the early evening when families are returning home from work and school. Throughout the operating day, but especially during these peak periods, it is normal for many wet wells (also sometimes referred to as stations or lift stations) to pump simultaneously into the same force main since there is no coordination between pumping stations.
The pressure caused by a fluid is sometimes referred to as head pressure. Accordingly, and with respect to force mains, the pressure within the force main may be referred to as head pressure. The more stations that simultaneously pump, the higher the head pressure within the force main. Pumps cannot pump efficiently when pumping against higher pressures. Smaller pumps may not be able to pump at all when more powerful pumps are dominating the force main. This may cause pumps to run longer in order to accomplish their purpose. This condition may result in drastically higher energy costs, increased wear and tear on pumps and mains, and a greater likelihood of failures of the pipes within the system which may, in turn, cause sewage spills. Conversely, there are also many periods during which no pumps are running. When wastewater generation is at the lowest volume, e.g., in the middle of the night or, perhaps at mid-morning or mid-afternoon (when many users of a wastewater treatment system are either at work or at school), the majority of pumping stations are frequently dormant.
Wastewater treatment plants are designed and sized either to accommodate estimated daily total inflows, or to serve peak demands on the wastewater treatment system. Plants designed to accommodate a daily average inflow run the risk of being incapable of handling those few peak hours of the day when most of the wastewater inflow occurs. One solution to this problem has been to design wastewater basins to temporarily hold overflow wastewater while capacity at the wastewater treatment plant is cleared. These wastewater basins are also sometimes referred to as surge basins. Surge basins can be costly to construct and can also be costly to maintain. Further, there can be health risks associated with surge basins that can be associated with untreated wastewater being stored within the sure basin for various amounts of time.
Those wastewater treatment plants that are designed to accommodate the peak inflow hours sit idle for most of the day, since the peak inflows only occur during a few hours out of a 24-hour operational day. Failure to provide sufficient capacity will likely result in pretreatment spills, damage to infrastructure which results in high repair costs and loss of service to customers, as well as possible damage to customer property. Wastewater treatment plants that are overdesigned, i.e. designed to meet the peak flow periods, can be wasteful of taxpayer dollars during the initial construction, can result in higher maintenance and operation costs, and also result in higher energy usage.
Very frequently, wastewater treatment plants are sized based on estimated daily total inflows and are measured in terms of millions of gallons per day (MGD). When, over a period of years, population increases exceed long-term plans, the addition of surge tanks to temporarily store the unmanageable inflow is necessary to prevent overflows at the point of inflow of the wastewater into the wastewater treatment plant, also known as the headworks. Later, during lower flow times, surge tank contents may be processed through the treatment system. Surge tanks provide temporary storage at the wastewater treatment plant to accommodate the wastewater plant's processing rate, but do not lessen flow into the infrastructure. Accordingly, although surge tanks address the issue of storing excess wastewater that needs to be treated, the problem of unmanageable flow of wastewater within a wastewater treatment system and, more particularly, within the pump stations and pipes that manage the flow of the wastewater to the wastewater treatment plants, remains unresolved.
Wastewater collection systems have pump stations distributed throughout the service area that arbitrarily pump wastewater to the wastewater treatment plants. The action of the pump stations may be characterized as arbitrary in that there is no coordination of the pumping function of one pump station with the pumping function of any other pump stations in a wastewater treatment system. These pumps only respond to local conditions and are activated by local level sensors without regard to events or conditions elsewhere. As a result, during peak activity hours, e.g., from 6 AM to 8 AM and from 5 PM to 7 PM, these pump stations operate more frequently, thereby raising the inflow into the plant, frequently surpassing the plant's processing capability. Even more troubling, however, is the excess flow of wastewater through the force main of the wastewater treatment plant. It should be noted that these high inflow periods normally occur between periods during which there is very little, if any, flow into the wastewater treatment plant. The result is normally a need for a higher design margin and/or earlier system expansion.
Another consequence of unmanaged flow is reduced efficiency in managing biological treatment material at the wastewater treatment plant. The most efficient biomass management requires a relatively constant flow rate so that bacteria used in processing the wastewater can effectively interact with the influent waste. High or irregular flow rates can lessen the efficiency of the treatment system and the quality of the treated effluent.
Sewer mains are frequently sized to take into account future growth in a wastewater collection service area, but it is not unusual for years to pass before the volume of wastewater reaches the level for which the system was designed. During this time, the utility may experience maintenance problems if the volume of wastewater through the main is not sufficient to carry with it solids and silt. If the flow of wastewater is so small relative to the pipe size that it fails to reach a velocity known as “scour speed,” solids may settle out of the liquid and accumulate in the bottom of the sewage mains. When this occurs, expensive specialty vehicles typically known as vacuum trucks are employed to clean out sediment that accumulates in the sewage system.
Accordingly, with the above in mind, it is noted that wastewater collection and treatment systems often operate under conditions in which pumps operate inefficiently, causing increased energy cost and wear and tear on costly equipment. It is further noted that peak flows into the treatment plant may result in accidental spillages and may impede the operational efficiency of the biological treatment processes utilized in the treatment plant. The above description also indicates that there are times when flow is inadequate to keep the force mains free of sediment, requiring the use of expensive special purpose trucks. In addition, the operational requirements of the various force mains may sometimes allows small pumps to run at the same time as larger pumps thereby causing the smaller pumps to operate against the higher pressure from the larger pumps resulting in considerable inefficiency in the operation of the smaller pumps. Also, existing systems frequently encounter situations where the wet wells to do not get pumped down sufficiently and therefore begin to generate septic conditions with the accompanying unpleasant smells. In light of the above deficiencies in the prior art, there exists a need for a flow management system that addresses the above referenced problems.